Population=[[400;120],zeros(2,30)];
for n=1:30;
    Population(1,n+1)=Population(1,n)*1.1;
    Population(2,n+1)=Population(2,n)*1.2;
end;

T=0:30;
semilogy(T,Population(1,:),'r');
hold on;
semilogy(T,Population(2,:),'b');
xlabel('time /day');
ylabel('parasite population');
legend('Myself','Assistant');